package main

import (
	"encoding/json"
	"fmt"
	"os"
)

/**
json的使用
*/

type response1 struct {
	Page   int
	Fruits []string
}
type response2 struct {
	Page   int      `json:"page"`
	Fruits []string `json:"fruits"`
}

func main() {
	//First we’ll look at encoding basic data types to JSON strings. Here are some examples for atomic values.

	bolB, _ := json.Marshal(true)
	fmt.Println(string(bolB))
	intB, _ := json.Marshal(1)
	fmt.Println(string(intB))
	fltB, _ := json.Marshal(2.34)
	fmt.Println(string(fltB))
	strB, _ := json.Marshal("gopher")
	fmt.Println(string(strB))
	//And here are some for slices and maps, which encode to JSON arrays and objects as you’d expect.

	slcD := []string{"apple", "peach", "pear"}
	slcB, _ := json.Marshal(slcD)
	fmt.Println(string(slcB))
	mapD := map[string]int{"apple": 5, "lettuce": 7}
	mapB, _ := json.Marshal(mapD)
	fmt.Println(string(mapB))
	//The JSON package can automatically encode your custom data types. It will only include exported fields in the encoded output
	// and will by default use those names as the JSON keys.

	res1D := &response1{
		Page:   1,
		Fruits: []string{"apple", "peach", "pear"}}
	res1B, _ := json.Marshal(res1D)
	fmt.Println(string(res1B))
	//You can use tags on struct field declarations to customize the encoded JSON key names.
	// Check the definition of response2 above to see an example of such tags.

	res2D := &response2{
		Page:   1,
		Fruits: []string{"apple", "peach", "pear"}}
	res2B, _ := json.Marshal(res2D)
	fmt.Println(string(res2B))
	//Now let’s look at decoding JSON data into Go values. Here’s an example for a generic data structure.

	byt := []byte(`{"num":6.13,"strs":["a","b"]}`)
	//We need to provide a variable where the JSON package can put the decoded data. This map[string]interface{} will hold
	// a map of strings to arbitrary data types.

	var dat map[string]interface{}
	//Here’s the actual decoding, and a check for associated errors.

	if err := json.Unmarshal(byt, &dat); err != nil {
		panic(err)
	}
	fmt.Println(dat)
	//In order to use the values in the decoded map, we’ll need to cast them to their appropriate type.
	// For example here we cast the value in num to the expected float64 type.

	num := dat["num"].(float64)
	fmt.Println(num)
	//Accessing nested data requires a series of casts.

	strs := dat["strs"].([]interface{})
	str1 := strs[0].(string)
	fmt.Println(str1)
	//We can also decode JSON into custom data types. This has the advantages of adding additional type-safety to our programs
	// and eliminating the need for type assertions when accessing the decoded data.

	str := `{"page": 1, "fruits": ["apple", "peach"]}`
	res := response2{}
	json.Unmarshal([]byte(str), &res)
	fmt.Println(res)
	fmt.Println(res.Fruits[0])
	//In the examples above we always used bytes and strings as intermediates between the data and JSON representation on standard out.
	// We can also stream JSON encodings directly to os.Writers like os.Stdout or even HTTP response bodies.

	enc := json.NewEncoder(os.Stdout)
	d := map[string]int{"apple": 5, "lettuce": 7}
	enc.Encode(d)
}
